1. Field of the Invention
Embodiments of the present invention relate to geographical information systems and applications.
2. Background Art
Geographical information is increasingly being made available to users in a variety of systems and applications. Geographical information can include terrain data representative of surface features including land and water surfaces. In many applications, terrain data can cover a large surface area such as a surface of the Earth. Different resolutions of the terrain data are used to facilitate rendering and viewing of the terrain data from different viewing distances relative to the terrain. Multi-resolutional terrain information can also be provided in tiles. Such tiles are especially helpful in many online geographical information systems or services, such as Google Earth, so that the most relevant geographical information to a location being viewed can be served to a remote client device for display.
In many instances, the amount of geographical information is large and may correspond to a curved surface, such as, all or part of the surface of the Earth or other body. Approximations are then needed especially when the geographical information needs to be sent over a network to remote users. For example, online geo-spatial applications render the intrinsically-curved surface of the Earth though a series of approximations, typically including the creation of a multi-resolution tiled triangle mesh, compression for network transmission, format and scale conversions for display using a graphics card, and distance from camera encoding in a frame buffer for depth comparison.
One approximation that has been used is a simple mesh simplification that simplifies a terrain mesh by removing less important primitives. This reduces the amount of detail available for rendering, but has the advantage of reducing the amount of mesh information that needs to be transmitted over a network to a client device.
As recognized by the inventors, however, such approximations and especially simple mesh simplification, have significant failings especially when rendering a water surface on a curved body or near land boundaries or shallow areas, such as, a shoreline.